It is known to prepare ketoximosilanes by reacting alkyltrichlorosilanes with ketoximes; see, for example, German Auslegeschrift No. 1 301 140, published European Application No. 0 082 324, Soviet Pat. No. 435 243 and Soviet Pat. No. 724 514. The performance of these processes always involves the risk that the ketoxime and ketoximosilane come in contact with inorganic substances of a strong acid nature. The resulting intermediate hydrogen chloride then forms the hydrochloride of the ketoxime. For example, methylethylketoxime boils under normal pressure at 152.degree. C. without decomposing, whereas the hydrochloride thereof vigorous decomposes at 50.degree. to 70.degree. C. Such decompositions, moreover, can be triggered by catalytic amounts of FeCl.sub.3, for example. Under such conditions, ketoximosilanes also tend to undergo explosive decompositions. L. J. Tyler reports on two violent explosions of this type in Chemical Engineering News, 52 (1974) 35, 3.
It is also known to prepare ketoximosilanes by reacting organosilanes with ketoximes in the presence of suitable acid acceptors and solvents; see, for example, U.S. Pat. Nos. 3,962,160, 3,441,583, 3,341,486, 3,817,909, German Auslegeschrift No. 1 301 140, German Auslegeschrift No. 1 255 924, French Pat. No. 1,118,495, European Pat. No. 0 036 262, and W. Noll, Chemie und Technologie der Silikone, page 342, published by Verlag Chemie, Weinheim 1968).
In these known processes, solid ammonium salts such as ammonium chloride or amine hydrochlorides are obtained as by-products, depending upon the type of acid acceptor which is used. These salts necessarily precipitate during the reaction in the form of a crystalline slurry. Once the reaction has gone to completion, the resulting oximosilane is separated from the precipitated salt, and subsequently the salt is washed again with large amounts of solvent. Since it is not possible to economically wash these salts such that they are absolutely clean, they introduce the disadvantage that they adsorb on their surface a significant amount of the desired end product, namely oximosilane.
The filtrate contains the desired oximosilane which remains in the sump after distilling of the solvent. A subsequent distillation of the particular ketoximosilane must be carried out in a vacuum, which is expensive and not without danger, because this process step already approaches the limit of thermostability of the ketoximosilane.